FIG. 1 is a block diagram which illustrates a wireless communication system 100. The system 100 includes a base station (BS) 130-1 that may communicate with wireless communication devices (WCD) 110 that are within downlink transmission range. The base station 130-1 may be connected to other base stations 130-2, 130-3, 130-4 via an Internet Protocol (IP) network 140 to provide wide area coverage thereby enabling the wireless communication devices 110-1, 110-2 to communicate with other wireless communication devices through other base stations 130-2, 130-3 and 130-4. Wireless communication devices 110 may roam between base stations 130-1, 130-2, 130-3 and 130-4 in order to provide mobility.
The base station 130-1 covers a certain geographic area and serves one or more wireless communication devices 110 (e.g., portable/mobile subscriber units, fixed subscriber units, and the like) that are associated with it and/or that are located within its downlink transmission range. As known in the art wireless communication devices 110 associate themselves to a particular base station by selecting the base station which produces the largest received signal strength (RSS) value. Additionally, after the association the wireless communication device 110 may exchange messages with a base station to complete a registration procedure. Generally speaking an association only method minimizes channel traffic and system complexity, while an association and registration method supports a more spectrally efficient usage of the channels in a wide area system. As used herein, the term “outbound” or “downlink” refers to a transmission path from a base station 130-1 to a wireless communication device 110. The area covered depends at least in part on the base station's transmit power. A base station 130-1 is normally capable of transmitting at much higher power than the wireless communication devices 110 and hence can cover a larger area on its downlink transmission. By contrast, the transmit power of a wireless communication device 110 is usually less than that of the base station 130-1, and therefore, the radio frequency (RF) coverage area on the uplink transmission path is limited in comparison to the downlink coverage area. As used herein, the term “inbound” or “uplink” refers to a transmission path from a wireless communication device 110 to the base station 130-1. This leads to an asymmetric transmission issue in any wireless system involving a base station 130-1 and wireless communication devices 110 that transmit at a lower power than the base station 130-1.
The base station 130-1 can be configured to transmit at different transmit power levels. In FIG. 1, constant Receive Signal Strength (RSS) contours 150, 160 are shown for two different transmit power levels of the base station 130-1. The downlink transmission range is dependent on output power level of the base station 130-1. When the base station 130-1 is configured for low power, then output power level of the inner contour 150 could be the same as that of the outer contour 160 when the base station 130-1 is configured for high power. Although the RSS contours 150, 160 are illustrated as being circular, it will be appreciated that this is done only for purposes of illustration, and that the RSS contours 150, 160 could be of any shape depending at least in part on the surrounding environment and the amount of fading the RF signal undergoes. Assuming that the transceiver and antenna characteristics of both wireless communication devices 110-1 and 110-2 are approximately the same, then the wireless communication devices 110-1 and 110-2 would observe approximately the same RSS level when on the same contour 150 or 160.
Although downlink transmissions from the base station 130-1 will often be received by both wireless communication devices 110-1, 110-2, uplink transmissions from the wireless communication device 110-2 may not be received by the base station 130-1 due to a difference in relative transmit powers. For instance, uplink transmission by the wireless communication device 110-1 on the inner contour 150 can reach the base station 130-1 since it is closer to the base station 130-1, but uplink transmission from the wireless communication device 110-2 on the outer contour 160 may not reach the base station 130-1 since its transmit power may not be adequate to reach the base station 130-1.
In other words, since base station 130-1 transmits at a relatively high power with respect to the wireless communication device, a wireless communication device 110-2 on a fringe area may be able to receive downlink (or outbound) transmissions from the base station 130-1, but its uplink (or inbound) transmissions to the base station 130-1 may not be able to reach the base station 130-1. Therefore, transmissions from the wireless communication device 110-2 may not be received by the base station 130-1. When a wireless communication device 110-2 receives downlink transmissions from the base station 130-1 with good RSS and the wireless communication device 110-2 is requested/required to transmit voice or data, the wireless communication device 110-2 will transmit on the uplink channel. However, the decision for the wireless communication device 110-2 to transmit on the channel does not take into account the ability of the wireless communication device 110-2 to communicate its uplink (or inbound) transmissions with the base station 130-1.
Techniques, such as forward error correction and diversity reception, can be implemented at the base station to improve reception of signals transmitted from the wireless communication device. However, these techniques can not be implemented in some systems because they are too processing intensive, and/or because the base station lacks multiple receiving antennas needed to implement diversity reception.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.